Medical biology

medical biology –first class
lecturer: dr. hanan selman
lectuer no. 1




biology ( bios : life , logia : science ) is a natural science concerned with the study of life and living organisms, including their structure, function, growth, evolution, distribution, and taxonomy. biology generally recognizes the cell as the basic unit of life, genes as the basic unit of heredity, evolution as the engine that propels the synthesis and creation of new species, also that all organisms survive by consuming and transforming energy and by regulating their internal environment to maintain a stable and vital condition. modern biology is a vast field, composed of many branches, such as cell biology, microbiology, genetic, immunology, parasitology histology etc. cell biology is a branch of biology deals with the study of cells from morphology, structure, function and biochemical point of views, the idea and concept of cell biology evolved during 19th century as a result of gradual advancement in the field of microscopy and biochemistry.

cell theory concept
the term "cell" was first introduced by the english scientist , robert hooke, in 1665 while he cut a slice of cork and examined under a simple microscope, he observed several honey comb like structures in the cork he gave the term cell (l. cella = compartment or small room) for each compartment. a few years later, anton van leeuwenhoek was the first examine a droping of pond water under the microscope, he observed many tiny, motile organisms he called them "animalcules" meaning little animals. leeuwenhoek, was also the first describing various forms of bacteria. in 1831 robert brown noticed a spherical body in the cell he gave it the name "nucleus”. in 1838, the german botanist schleiden reported that all plant tissues were composed of cells and he was considered to be the founder of the cell theory, then after one year 1839, the german zoologist schwann extended the finding of schleiden to the animal tissues and both proposed the basis of cell theory .
the modern form for the cell theory states that:
“the body of all living organisms is composed of cells, cell products and new cells are produced by the division of the pre – existing ones".
today the cell theory includes four ideas:
• the cells are the building block of structures in living things
• the new cell is derived from other cells by division
• the cell contains information that is used as instructions for growth, development and functioning
• the cell is the functioning unit of life and the chemical reactions of life take place within cells.


the microscope
microscope (from the greek, micro, small and scope to look or see) is an instrument used to examine the objects that are too small for naked eyes because the small dimensions of majority of cells between (10-150) ?m and transparent nature of cell and its organelles cause problems to cell biologists when trying to understand its organization and functioning.
the system international (si) units of length are:
1 metre (m) = 1000 millimetres (mm)
1 m = 1000 micrometres (?m)
1 ?m = 1000 nanometres (nm)
1 nm = 1000 picometres (pm)
the angstrom (?) = 10- 10 m

the first useful compound microscope was invented by francis janssen and zacharias janssen in 1590 it had two lenses with magnification powers between 10x and 30x. galileo galilei (1564 - 1642) invented a simple microscope to study the compound eye of insects his microscope had only one magnifying lens (fig.). marcello malpighi (1628-1694) an italian microanatomist used a microscope to study organ tissues of animals. robert hooke an english microscopist in 1665 examined a slice of cork tissue under a compound microscope designed by him. anton van leeuwenhoek (1632-1723) improved the quality of lenses used in microscopes with magnification up to 300x. further advancements in cell biology were made by improving the quality of compound microscopes.





















fig. optical microscope







a- compound light microscope

several types of light microscope are commonly used in the lab. are:

1-the bright – field microscope
the ordinary microscope is called bright – field microscope because it forms a dark image against a brighter background , it is consist of two series of lenses objective and ocular lenses which function together to resolve the image (fig.) with this microscope , specimens are render visible because of the differences in contrast between them and surrounding medium ,dyes can be used to stain cells or their organelles increase their contrast so, they can be easily seen in this microscope . this microscope generally employ 4x , 10x , 40x , 100x power objective lenses with a 10x power ocular lens , thus magnifying the specimens 40 , 100 , 400 , 1000 times .

2-dark – field microscope
it is an ordinary microscope to which a special condenser is attached , the condenser serves to intensify illumination of the examined specimen through narrow area , this creates a " dark field" that contrasts against the high light edge of the specimens .this technique has been useful for observing organisms such as treponema palladium a spirochetes which is less than 0.2 µm in diameter .

3- fluorescence microscope
the fluorescence microscope is used to visualize specimens that fluoresce, which is the ability to absorb short wavelengths of light (ultraviolet) and give off light at a longer wavelength (visible).















fig. : the bright – field microscope




4- phase- contrast microscope
it is an ordinary microscope in which modified objective lenses and condensers are used to permit direct examination of living cells without fixation or staining, this microscope takes advantage of the fact that light waves passing through transparent objects such as cells emerge in different phases depending on the properties of the materials through which they pass .

b- the electron microscope
the high resolving power of the electron microscope has enabled scientists to observe the minute details structures of cells .the superior resolution of the electron microscope is due to the fact that electrons have a much shorter wavelength than the wavelength of photon’s light.
there are two types of electron microscope:

1- transmission electron microscope (tem)
it is a first to be developed by employs a beam of electrons projected from an electron gun directed and focused by an electromagnetic condenser lens on a thin specimen. tem can resolve particles 0.001µm apart, viruses with diameter 0.01 -0.2 µm can be easily resolved.

2- scanning electron microscope (sem)
sem is generally has a lower resolving power than tem, however, it is particularly useful for providing three – dimensional images of the surface of microscope objects, it can resolve features as small as 5 nm.


















fig. scanning electron microscope photo




microorganisms and all other living organisms are classified as prokaryotes or eukaryotes on basis of their cellular characteristics , for example prokaryotic cells ( pro : before , karyon : nucleus ) lack a true nucleus and complex membrane-bound organelles, while eukaryotic cells (eu: true, karyon : nucleus) have both true nucleus and complex organelles e.g., mitochondria, endoplasmic reticulum, centrioles, lysosomes, golgi complexes etc. an essential feature of most living cells (prokaryote and eukaryote) is their ability to grow in an appropriate environment and to undergo cell division. prokaryotic and eukaryotic cells are similar in several ways, both types of cells are enclosed by cell membranes (plasma membranes have non – membranous organelle ribosome for protein synthesis and are using dna for their genetic information. prokaryotes such as bacteria and cyanobacteria. eukaryotes such as animal, plant, fungi, protozoa, while viruses are considered neither prokaryotes nor eukaryotes because they lack the characteristics of living things, except ability to replicate which they accomplish only in living cells.
there are fundamental differences in eukaryotic and prokaryotic structure:




















fig. prokaryote and eukaryote cell







table: the differences between prokaryote and eukaryote cell

characteristic prokaryotes
bacteria eukaryote
animal plant

nuclear membrane no yes yes
plasma membrane yes yes yes
cell wall yes no yes
ribosome
yes yes yes
endoplasmic reticulum no yes yes
golgi complex no yes yes
lysosomes no yes yes
peroxisomes no yes yes
nucleolus no yes yes
mitochondria no yes yes
chloroplasts no no yes
cilia/flagella yes yes no
microtubules no yes yes
chromosome
single multiple multiple